One dimensional (1D) nanostructures represent attractive building blocks for nanoscale optoelectronic devices. Among these 1D nanostructures, photoconductive materials have drawn intensive interests for their applications in photodetectors, optical switches and sensors. To date, most of these nanodevices are fabricated from inorganic nanowires and carbon nanotubes, whereas only a few such photoconductive 1D nanostructures have been reported for organic materials, despite having various advantages over their inorganic counterparts including chemically tunable electronic and optical properties and conformal flexibility and adaptability. Moreover, among the limited number of 1D organic nanomaterials that demonstrated photoconductivity response, most of them are a p-type semiconductor, i.e. the hole acts as the transporting charge carrier. This is partially due to the limited availability of air-stable n-type organic materials.
One way to approach high photoconductivity response is to fabricate the 1D nanomaterials from building-block molecules that contain covalently linked electron donor (D) and acceptor (A) units, for which efficient charge separation can be initiated upon photoexcitation. However, assembling the covalently linked D/A molecules into continuous 1D stacks remains challenging, as the strong charge transfer interaction between the D/A moieties often causes them to stack on each other, producing a bulk-mixed phase, where the rapid charge recombination between D+ and A− dominates the loss of photogenerated charge carriers. While instant photoinduced charge separation can be achieved for many D/A systems, the subsequent long-range intermolecular charge transport (towards the electrodes) is often a bottleneck for approaching high efficiency of photocurrent generation. To date, only few D/A molecules have successfully been fabricated into segregated, highly organized phases that can afford high photoconductivity.
Compared to the inorganic chemiresistors, organic semiconductors offer not only facile deposition procedure, but various choice and easy tuning of bind receptors for analyte molecules. However, the drawback for using organic semiconductor materials in the same chemiresistor based sensors is their poor conductivity. Although organic field-effect transistors (FETs) can be used as sensors in the similar way as worked for chemiresistors, the fabrication of such FETs is relatively complicated and the performance is affected by many factors, like boundary grain, surface morphology, molecular structure etc.